1. Field of the Invention
This invention relates in general to a method and apparatus for subaqueous pile driving at considerable depths, and more specifically comprises a ship equipped with a lifting crane and a pile driving head, said head being vertically reciprocable in a subframe coupled to the crane. The pile driving apparatus is guided on cables connected to the pile and running downwards from the ship.
2. Description of the Prior Art
Copending application Ser. No. 588,554 filed on June 19, 1975 and now U.S. Pat. No. 3,998,064 discloses a submergible pile driving apparatus in which the subframe acts as a means to keep the pile in an upright position at the beginning of the pile driving process. The subframe is guided on the pile, the pile driving head is guided in the subframe, and the subframe is suspended from the lifting crane by means of a cable. In addition, the subframe and the pile driving head are guided on cables connected to the pile, said cables serving as a guide during the lowering of the pile driving head and the subframe onto the pile head. During the process of pile driving, however, the cables no longer serve as a guide and are slack and relieved from stress, so that they are not affected by impact loads that occur during the pile driving process.
During submerged pile driving the pile driving head must be supplied with hydraulic energy for its operation, and there should be a hydraulic return line. Electric lines are also required for carrying out measurements which may be read on the ship so that the personnel in charge can properly monitor and control the operation. Underwater television may be provided, and compressed air must be supplied to the casing embracing the pile driving device to provide air in the region where the ram strikes the head of the pile. At a considerable driving depth this means that considerable lengths of several hoses have to be lowered, which not only requires large reels with a full stock of hoses but results in the hoses easily becoming entangled. Further, the cable on which the pile driving apparatus is suspended is flexible and presents an obstruction over a considerable portion of its length. The flexible cable also permits the pile driving apparatus to rotate about the vertical axis, which increases the problems that already exist with hoses.